Photocollographic printing plate and method for producing the same



April 19, 1927.

M. DE SPERATI PHOTOCOLLOGRAPHIC PRINTING PLATE AND METHOD FOR PRODUCINGTHE SAME Filed May 12, 1926 lit ' WEE-5,714

anraito an srnaaar, or TURIN', irarrr, .assrenoia 'ro aneniwroennrnrca(70'. s. a.) ariuirnn, or Lennon, ENGLAND, A com any. or ENGLAND.

PHfiWQQQLLG'GRWHIG PRINTING PLATE AND METHOD FOR PRODUCING THE SAME.

application filed may 12, 1926, Serial No. 108,616, and in Italy May 3,1925.

The present invention relates to printing plates obtained by the actionof light on a colloidal layer located on a support.

This invention has for its object an im- 8 proved printing plate of theabove stated character and a method of making the same.

According to the present invention the improved printing plate comprisesa layer of colloidal material which, in its portion 10 adjacent to'itssupport, is evenly impervious to moisture, whereas its surface portionor skin is differentiated to provide dots, lines or spots which are hardand impervious to moisture, and therefore in condition to take up ink,and also to provide dots, lines or spots which are slightly pervious tomoisture'and therefore are in condition to absorb an amount of moistureduring the printing I operation according to known "lithographicprocesses, thus producing the white portions of the image.

In the annexed drawing, Figures 1 and 2 represent by way of illustrationenlarged fragmental transverse sections of different 2 platesconstructed according to this invention. In Figure 1, -a isa supportwhich I ma be of celluloid, or of any other matonal, while -Z is a layerof colloidal mater'al applied on said support.

' When the plate is ready or printing, as shown on the drawing, afterthe treatment hereinafter described the layer -lcomprises a portion orsheet -b-- adjacent to support ar, which portion, throughout its entireextent is impervious to moisture; and to this portion or sheet b areconnected projectin portions 0- which are made ard an impervious likethe underlying 4o sheet -b-- and are encircled by portions dwhere. thecolloidal matter is in its original condition that is, it is soft andpervious to moisture.

In portions cthe colloidal light sensitive material has been acted on bylight at the time of exposure under a negative,

and their outer surface is in condition to take up ink; whereas inportions d the colloidal material has not been acted on by light andtherefore these portions d are able to absorb moisture and repel ink.

The word sheet, as used herein and in the appendedclaims, is intended todenote a portion of the layer extending over the entire surface of theplate and having a -to be worn out in printing machinery.

different character from adjacent similar portions or sheets, withoutnecessarily implying that each sheet is physically. separated ordistinct from the adjacent ones.

In the left-hand portion of Figure 1 the skin sheet of the layer hasdots of small size giving a white portion in the image when printed; theintermediate portion thereof has an intermediate tone, and theright-hand portion has'large hard spots giving a dark portion in thefinal image.

As shown in Figure 1, the portions dof colloidal material which are leftpervious, extend through a small fraction only of the layer -l which hasa comparatively great thickness. I

This feature has the advantage of remov ing difliculties found inproducing exceed ingly thin layers, which are inherently liable- Furtherit provides a satisfactory adhesion of the colloidal layer l: on thesupport a and prevents said layer from becoming detached from itssupport during the printing operations on account of moisture absorbedby portions d, because the I moisture absorbed by said portions -d-.- issmall owing to their reduced thiclmess and because it cannot reach theregion where j the layer sheet b contacts with support Finally, owing tocontraction of the col-" loidal material under the action of thealkaline bichromate treatment, the surface is made somewhat depressed atthe portions 0 with respect to portions --dand thus these depressedportions -0 are enabled to retain large quantities of ink, this featureimproving the sharpness and uniformity of prints.

To produce a printing plate of the described character, a plate or afilm is used, having a comparatively thick layer of emulsion which maybe obtained by usual mechanical means as known in connection with themanufacture of photographic films.

In Figure 2 the bottom sheet Z- consists of a plurality of sheets bb'having difi'erent degrees of hardness and imperviousness to moisture.

Hereinafter 'is described by way of example a preferred method for thepreparation of a late according to this invention.

.On a (re luloid sheet, which has been previously treated in knownmanner to improve sheets or layers.

the adhesion of the colloidal layer to be applied thereon, there isspread an emulsion of first-class gelatin having the desired th1ck vness, which may be about 20 or 30 thousandths of a millimetre, either byspreading a layer in a single operation, or by spreading a number oflayers one upon another, as described in connection with Figure 2.

The completed layer must have its maximum degree of imperviousness tomoisture near the support and its minimum most reduced degree ofimperviousness on its outer surface or skin, this being obtained, in themulti-layer construction, by first applying on the support a sheet orlayer of chemically hardened gelatin and then superimposing on the samemore and more pervious In case the layer is made in a single operation(that is, by spreading a single layer), the same requirement may becomplied with by sensitizing the emulsion when dry by means of asolution of alkaline bichromate, and by exposing the film to light fromits back for a time sufficient to make the emulsion impervious tomoisture to a gradually decreasing extent from the back portion of thelayer contacting with the support towards its outer skin.

By means of the described treatment, which must be completed by awashing operation to remove the yellow colour and the soluble chromiumsalts left in said layer, a layer of emulsion. is obtained having itsmaximum hardness in its portion contacting with the support while itshardness progressiyely decreases toward its outer surface or Forpreparing a printing plate for printing operation, a film having a layerof colloidal material obtained in the described manner is firstlytreated in a hardening bath say a 5% formalin bath, and then is washedabout 10 minutes; then it is sensitized by (1 means of an alakalinebichromate solution, preferably of ammonium, say a 3% solution, and itis finally dried while protected against light and dust.

The film thus obtained may then be exposed under a negative plate whichmay be a dotted or reticulated or grained one, or f which may also be ahalf tone negative; the exposure may be very short, as it is onlyrequired to act on the skin or surface of the sensitized gelatin layer.

When the plate is intended for direct printing on paper, no furtheroperation is required before washing; on the contrary when the plate isintended to be used in an indirect-printing or offset machine, it isadvisable to subject the plate to further exposure to li ht from theback, for a time about one third that of the exposure under f thenegative plate, so as to increase the thickness of the sheet --bwhich isevenly hardened and made impervious, and thusreduce the thickness ofportions -cl wh1ch are left somewhat pervious to water.

The film is finally thoroughly washed, for

about two hours, to remove the soluble chromium salts, and is ready forprinting.

The plate obtained in the described manner is printed in the usual wayfollowed in lithographic processes, that is, it is moistened after eachinking and printing operation; then it provides, with usual lithographicinks, very sharp and strong images by a single printing operation.

After printing has been started, the moistening operation at eachprinting operation may be replaced by or alternated with an exposure tomoist air.

WVhat I claim as my invention and desire to secure by United StatesLetters Patent 1. A printing plate comprising a support, a layer ofcolloidal material on said support, said layer comprisin a moistureimpervious sheet immediately a jacent to said support and a moisturepervious sheet on its skin or surface remote from said sup ort, saidmoisture pervious sheet having de ite, relatively small hard andimpervious spots for inking and printing purposes.

2. A printing plate comprising a support, a layer of colloidal materialon said support, said layer comprising a moisture impervious sheetimmediately adjacent to said sup ort and a moisture pervious, sheet onits s in, said moisture pervious sheet comprising definite,relatively-small hard and impervious spots obtained by li ht action andintegrally connected with said impervious sheet.

3. A printing plate comprising a translucent support, and a layer oflight-sensitive material on said support; said layer having its skinsurface rendered hard and moisture im ervious to different extents atdifferent e ite spots, and having its inner surface evenly hard andmoisture impervious, said evenly hard and moisture impervious innersurface being integrally connected with said hard and moistureimpervious skin spots.

4. A method of makin printing plates, comprising the steps of ormingupon one ace of a translucent support a layer of lightsensitive materialhaving its maximum and minimum degrees of imperviousness to moisturelocated, respectively, adjacent said support and atits outer surface orskin; sensitizing said layer; and ex osing said layer to light under anegative plate to form on the said outer surface or skin of the layerdefinite, relatively-small hard and impervious spots for inking andprinting pur uses;

5. A method of makin printing p ates, comprising the steps of ormingupon one ace of a translucent support a layer of lightsensitive materialhaving its maximum and minimum degrees of impervionsness to moisturelocated, respectively, adjacent said support and at its outer surface orskin; sensi-.

tizing said layer; exposing the outer surface or skin of the layer tolight under a negative to form thereon definite, relativelysmall hardand impervious spots for inking and printing purposes; and exposing saidlayer to light through said support to render its inner surface evenlyhard and moistureimpervious.

6. A method of making printing plates, comprising the steps of coating asupport with a layer of colloidal material; treating said layerphotochemically to render its back, for the greatest part thereof, hardand impervious to moisture, while leaving at its outer surface anextremely thin skin which remains pervions; sensitizing said skin; and

exposing said layer behind a negative, with the sensitized skin incontact therewith.

7. A method of making printing plates,

comprising the steps of coating a translucent support with a layer ofsensitized colloidal material; exposing the coated support to light fromthe back so as to harden said layer with the exception of an extremelythin skin at its outer surface which remains pervious to moisture;washing said layer and then sensitizing it again; exposing said skin tolight behind a negative to differentiate it in hardened portions andportions pervious to ink; and then printing.

8. A printing plate comprising a support; and a layer of colloidalmaterial on the sup port which is hardened and impervious tomoisturewith the exception of an extremely thin superficial skin that isdifierentiated in hardened portions and pervious portions to form theprinting surface,

In testimony whereof I aflix my signature.

MARIANO 1m SPERATI.

